This invention relates to an ignition timing control system for internal combustion engines, and more particularly to an ignition timing control system for controlling ignition timing on the basis of a signal indicative of the crank angle position of a crankshaft sensed by a magnetic pick-up.
In controlling the ignition timing of an internal combustion engine, a mixture supplied to the engine is ignited through a procedure which generally includes sensing predetermined crank angle positions of the engine crankshaft, calculating ignition timing conforming to engine operating conditions with reference to each of the predetermined crank angle positions, generating an ignition command signal based on the calculated ignition timing, and terminating supply of a pulse of electric current to the primary side of the ignition coil upon generation of the ignition command signal to cause generation of a high-voltage on the secondary side of the ignition coil, and thereby produce a spark discharge at a spark plug of the engine.
In order to ignite the mixture supplied to the engine precisely at the desired crank angle position, an ignition timing control system such as disclosed in Japanese Provisional Utility Model Publication (Kokai) No. 55-163476 is adapted to correct the ignition timing for a delay in time between the moment the ignition command signal is generated for the ignition coil and the moment the spark discharge is actually produced at the spark plug. However, in an arrangement which uses a sensor such as a magnetic pick-up to magnetically sense the crank angle position of the crankshaft in the ignition procedure described above, it is also necessary to take into account a time delay involved in the generation of the sensor output signal. Though this time delay can be shortened or substantially eliminated by employing a sensor that senses the crank angle position by optical means, such a sensor is high in cost and involves peripheral circuitry of some complexity.